001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 *  Unless required by applicable law or agreed to in writing, software
012 *  distributed under the License is distributed on an "AS IS" BASIS,
013 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 *  See the License for the specific language governing permissions and
015 *  limitations under the License.
016 */
017package org.apache.bcel.classfile;
018
019import java.io.DataInput;
020import java.io.DataOutputStream;
021import java.io.IOException;
022import java.util.HashMap;
023import java.util.LinkedHashMap;
024import java.util.Map;
025import java.util.Objects;
026
027import org.apache.bcel.Const;
028
029/**
030 * Extends the abstract {@link Constant} to represent a reference to a UTF-8 encoded string.
031 * <p>
032 * The following system properties govern caching this class performs.
033 * </p>
034 * <ul>
035 * <li>{@link #SYS_PROP_CACHE_MAX_ENTRIES} (since 6.4): The size of the cache, by default 0, meaning caching is
036 * disabled.</li>
037 * <li>{@link #SYS_PROP_CACHE_MAX_ENTRY_SIZE} (since 6.0): The maximum size of the values to cache, by default 200, 0
038 * disables caching. Values larger than this are <em>not</em> cached.</li>
039 * <li>{@link #SYS_PROP_STATISTICS} (since 6.0): Prints statistics on the console when the JVM exits.</li>
040 * </ul>
041 * <p>
042 * Here is a sample Maven invocation with caching disabled:
043 * </p>
044 *
045 * <pre>
046 * mvn test -Dbcel.statistics=true -Dbcel.maxcached.size=0 -Dbcel.maxcached=0
047 * </pre>
048 * <p>
049 * Here is a sample Maven invocation with caching enabled:
050 * </p>
051 *
052 * <pre>
053 * mvn test -Dbcel.statistics=true -Dbcel.maxcached.size=100000 -Dbcel.maxcached=5000000
054 * </pre>
055 *
056 * @see Constant
057 */
058public final class ConstantUtf8 extends Constant {
059
060    private static final class Cache {
061
062        private static final boolean BCEL_STATISTICS = Boolean.getBoolean(SYS_PROP_STATISTICS);
063        private static final int MAX_ENTRIES = Integer.getInteger(SYS_PROP_CACHE_MAX_ENTRIES, 0).intValue();
064        private static final int INITIAL_CAPACITY = (int) (MAX_ENTRIES / 0.75);
065
066        private static final HashMap<String, ConstantUtf8> CACHE = new LinkedHashMap<String, ConstantUtf8>(INITIAL_CAPACITY, 0.75f, true) {
067
068            private static final long serialVersionUID = -8506975356158971766L;
069
070            @Override
071            protected boolean removeEldestEntry(final Map.Entry<String, ConstantUtf8> eldest) {
072                return size() > MAX_ENTRIES;
073            }
074        };
075
076        // Set the size to 0 or below to skip caching entirely
077        private static final int MAX_ENTRY_SIZE = Integer.getInteger(SYS_PROP_CACHE_MAX_ENTRY_SIZE, 200).intValue();
078
079        static boolean isEnabled() {
080            return Cache.MAX_ENTRIES > 0 && MAX_ENTRY_SIZE > 0;
081        }
082
083    }
084
085    // TODO these should perhaps be AtomicInt?
086    private static volatile int considered;
087    private static volatile int created;
088    private static volatile int hits;
089    private static volatile int skipped;
090
091    private static final String SYS_PROP_CACHE_MAX_ENTRIES = "bcel.maxcached";
092    private static final String SYS_PROP_CACHE_MAX_ENTRY_SIZE = "bcel.maxcached.size";
093    private static final String SYS_PROP_STATISTICS = "bcel.statistics";
094
095    static {
096        if (Cache.BCEL_STATISTICS) {
097            Runtime.getRuntime().addShutdownHook(new Thread(ConstantUtf8::printStats));
098        }
099    }
100
101    /**
102     * Clears the cache.
103     *
104     * @since 6.4.0
105     */
106    public static synchronized void clearCache() {
107        Cache.CACHE.clear();
108    }
109
110    // for access by test code
111    static synchronized void clearStats() {
112        hits = considered = skipped = created = 0;
113    }
114
115    /**
116     * Gets a new or cached instance of the given value.
117     * <p>
118     * See {@link ConstantUtf8} class Javadoc for details.
119     * </p>
120     *
121     * @param value the value.
122     * @return a new or cached instance of the given value.
123     * @since 6.0
124     */
125    public static ConstantUtf8 getCachedInstance(final String value) {
126        if (value.length() > Cache.MAX_ENTRY_SIZE) {
127            skipped++;
128            return new ConstantUtf8(value);
129        }
130        considered++;
131        synchronized (ConstantUtf8.class) { // might be better with a specific lock object
132            ConstantUtf8 result = Cache.CACHE.get(value);
133            if (result != null) {
134                hits++;
135                return result;
136            }
137            result = new ConstantUtf8(value);
138            Cache.CACHE.put(value, result);
139            return result;
140        }
141    }
142
143    /**
144     * Gets a new or cached instance of the given value.
145     * <p>
146     * See {@link ConstantUtf8} class Javadoc for details.
147     * </p>
148     *
149     * @param dataInput the value.
150     * @return a new or cached instance of the given value.
151     * @throws IOException if an I/O error occurs.
152     * @since 6.0
153     */
154    public static ConstantUtf8 getInstance(final DataInput dataInput) throws IOException {
155        return getInstance(dataInput.readUTF());
156    }
157
158    /**
159     * Gets a new or cached instance of the given value.
160     * <p>
161     * See {@link ConstantUtf8} class Javadoc for details.
162     * </p>
163     *
164     * @param value the value.
165     * @return a new or cached instance of the given value.
166     * @since 6.0
167     */
168    public static ConstantUtf8 getInstance(final String value) {
169        return Cache.isEnabled() ? getCachedInstance(value) : new ConstantUtf8(value);
170    }
171
172    // for access by test code
173    static void printStats() {
174        final String prefix = "[Apache Commons BCEL]";
175        System.err.printf("%s Cache hit %,d/%,d, %d skipped.%n", prefix, hits, considered, skipped);
176        System.err.printf("%s Total of %,d ConstantUtf8 objects created.%n", prefix, created);
177        System.err.printf("%s Configuration: %s=%,d, %s=%,d.%n", prefix, SYS_PROP_CACHE_MAX_ENTRIES, Cache.MAX_ENTRIES, SYS_PROP_CACHE_MAX_ENTRY_SIZE,
178            Cache.MAX_ENTRY_SIZE);
179    }
180
181    private final String value;
182
183    /**
184     * Initializes from another object.
185     *
186     * @param constantUtf8 the value.
187     */
188    public ConstantUtf8(final ConstantUtf8 constantUtf8) {
189        this(constantUtf8.getBytes());
190    }
191
192    /**
193     * Initializes instance from file data.
194     *
195     * @param dataInput Input stream
196     * @throws IOException if an I/O error occurs.
197     */
198    ConstantUtf8(final DataInput dataInput) throws IOException {
199        super(Const.CONSTANT_Utf8);
200        value = dataInput.readUTF();
201        created++;
202    }
203
204    /**
205     * @param value Data
206     */
207    public ConstantUtf8(final String value) {
208        super(Const.CONSTANT_Utf8);
209        this.value = Objects.requireNonNull(value, "value");
210        created++;
211    }
212
213    /**
214     * Called by objects that are traversing the nodes of the tree implicitly defined by the contents of a Java class.
215     * I.e., the hierarchy of methods, fields, attributes, etc. spawns a tree of objects.
216     *
217     * @param v Visitor object
218     */
219    @Override
220    public void accept(final Visitor v) {
221        v.visitConstantUtf8(this);
222    }
223
224    /**
225     * Dumps String in Utf8 format to file stream.
226     *
227     * @param file Output file stream
228     * @throws IOException if an I/O error occurs.
229     */
230    @Override
231    public void dump(final DataOutputStream file) throws IOException {
232        file.writeByte(super.getTag());
233        file.writeUTF(value);
234    }
235
236    /**
237     * @return Data converted to string.
238     */
239    public String getBytes() {
240        return value;
241    }
242
243    /**
244     * @param bytes the raw bytes of this UTF-8
245     * @deprecated (since 6.0)
246     */
247    @java.lang.Deprecated
248    public void setBytes(final String bytes) {
249        throw new UnsupportedOperationException();
250    }
251
252    /**
253     * @return String representation
254     */
255    @Override
256    public String toString() {
257        return super.toString() + "(\"" + Utility.replace(value, "\n", "\\n") + "\")";
258    }
259}